With the advent of low lead gasoline, it is now common practice to provide hardened valve seats in internal combustion engines. In this manner, the valve seats have a better wear characteristic and can withstand the constant pounding by a poppet valve. This is needed because the lubricating effect of lead and phosphorous in the gasoline being consumed is no longer available. Several concepts have been used in providing such hardened valve seats. One of these is to utilize hardened inserts to define the valve seats themselves. Of course, this solution presents obvious difficulties in that the valve seats are more expensive and require substantially more manufacturing and assembling costs. The most common approach is to inductively heat the conical surface forming the valve seat of an internal combustion engine by positioning an inductor adjacent the seat and directing high frequency currents through the inductor. After the inductor has been energized to heat the valve seats inductively, the heating operation is discontinued. At that time, the valve seat is quenched, generally by mass quenching which results from conduction of heat from the valve seat rapidly into the surrounding metal. In high production, it is desirable to heat all valve seats at the same time for subsequent quench hardening by liquid or mass cooling.
U.S. Pat. No. Re. 29,046 illustrates a machine for inductively heating several valve seats simultaneously. In accordance with the teachings of this prior patent, incorporated by reference herein, a plurality of floating inductor assemblies are provided in a plurality of housings which are movable toward and away from respective valve seats of an engine component. Each of the inductor assemblies includes an inductor loop at one end of a carrier and a nose concentric with the loop extending toward the valve seat. This nose contacts the valve bore in the engine component to center the respective inductor carriers with respect to the valve seat preparatory to induction heating. This action occurs when the housings carrying the respective inductor assemblies are moved toward the valve seats. By using the inductor carrier and nose which enter the bore, each of the inductor assemblies is centered with respect to the particular valve seat to be heated, irrespective of certain manufacturing tolerances between adjacent valve seats.
After the housings move the carriers into the position with the inductors concentric with the valve seats, the motion of the housing toward the valve seats continues until the inductors actually engage the valve seats. Thereafter, the various housings carrying the inductor assemblies are locked together and moved in unison away from the engine component a distance corresponding to the desired air gap for proper induction heating. In this manner, the machine compensates for axial offset of the respective valve seats being processed during a given cycle. To allow for radial alignment of the respective inductor assemblies with respect to the valve seats as the aligning noses enter the valve bore, each of the inductor assemblies floats within their respective housings in a manner to allow movement only in the radial direction. To accomplish this, a flange is provided around the inductor carrier of the inductor assembly. This flange is clamped within a companion housing to allow only radial movement. During processing of the valve seats, the inductor at the end of the inductor assembly is properly positioned in the radial direction and in the axial direction for the desired heating of the valve seats. This prior machine has been exceedingly successful and is generally used throughout the automotive industry.
As the engines being used in automobiles are reduced in size, the spacing between adjacent valve seats to be hardened has been reduced. Consequently, the prior housings carrying the floating inductor assemblies were too large to allow the desired small spacing between the adjacent inductors. This problem was solved in one of two ways. Either the engine component was processed twice so that only alternate valve seats were hardened during a heating cycle or the floating inductor assemblies were machined so that the inductor and nose were offset from the primary axis of the total floating inductor assembly. Each of these solutions had disadvantages. If the engine component required two cycles for processing its valve seats, the production rate was substantially reduced. If offset inductor assemblies were provided, it was necessary to provide different structures for the inductor assemblies used at adjacent valve seats. Consequently, at least twos designs had to be manufactured and stockpiled. Also, even with the offset inductors, it was not always possible to simultaneously process the valve seats of the head of a relatively small engine.